Since at least 1974, the General Electric Corporation has worked in the area of making bodies of silicon carbide material by pressureless sintering techniques. Basically, they have proposed that one begin the manufacture of such bodies using submicron beta silicon carbide powder. That powder may be subjected to an operation to form it into a consolidated mass, for example, a slip casting operation or a pressing operation. After the submicron beta silicon carbide powder is consolidated, General Electric has taught that the material should be heated to a temperature in excess of 2000.degree. C. for a period of time of about 1 hour in order to achieve a sintering of the individual beta silicon carbide particles into a single unitary body.
In a paper entitled "Microstructures of Sintered Silicon Carbide" as reported in Ceramic Microstructures, Proceedings of the 6th International Materials Symposium, Westview Press, Colorado (1977), Messrs. C. A. Johnson and S. Prochazka of the General Electric Corporate Research and Development report, beginning at page 366, that large feathery-like alpha silicon carbide platlet grains are developed when beta silicon carbide powder is sintered together. The paper describes that these feathered grains reduce the strength of the overall body. Their paper also indicates that these platlets are formed by what they believe to be a combination of excessively high temperatures and certain chemical impurities such as aluminum.
In my work in this area, I have found that these enlarged platlets can be avoided in a sintering operation if that sintering operation is carried out under certain conditions to be described herein. Thus, even though the powders which I worked upon had the same impurities as contained in the powders worked on by the General Electric personnel, because the powders came from the same common General Electric source, I can now state that the impurities contained in these powders do not generate the particular feathery microstructure. The particular feathery microstructure is generated solely because of the temperature regime in which the prior art suggested that the sintering of such material be carried out. When this material is heated to a temperature in excess of about 1920.degree. C., a temperature lower than the lowest of 2000.degree. C. suggested in the art, I have found that the feathery microstructure is produced, and is produced in a manner in which substantially large grains of such material are found in the microstructure.